AS3911 datasheet(19/159 Pages) AMSCO

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[v2-11] 2016-Jun-13

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AS3911 − Application Information

Procedure to implement the slow transition:

• When transmitter is disabled set IO Configuration Register

2 bit slow_up to 1. Keep this state at least 2 ms to allow

discharge of VSP_RF.

• Enable transmitter, its output will ramp slowly.

• Before sending any command set the bit slow_up back

to 0.

Receiver

The receiver performs demodulation of the transponder

sub-carrier modulation which is superimposed on the

13.56MHz carrier frequency. It performs AM and/or PM

demodulation, amplification, band-pass filtering and

digitalization of sub-carrier signals. Additionally it performs

RSSI measurement, automatic gain control (AGC) and Squelch

function.

In typical application the Receiver inputs RFI1 and RFI2 are

outputs of capacitor dividers connected directly to the

terminals of antenna coil. Such concept assures that the two

input signals are in phase to the voltage on antenna coil. Care

has to be taken during design of capacitive divider that the RFI1

and RFI2 input signal pp value does not exceed the VSP_A

supply voltage.

Receiver comprises two complete receive channels for AM

demodulation and PM demodulation. In case both channels are

active the selection of channel used for reception framing is

done automatically by receive framing logic. The receiver is

switched on when Operation Control Register bit rx_en is set to

one. Additionally the Operation Control Register contains bits

rx_chn and rx_man; rx_chn defines whether both, AM and PM,

demodulation channels will be active or only one of them, while

bit rx_man defines the channel selection mode in case both

channels are active (automatic or manual). Operation of the

Receiver is controlled by four Receiver Configuration registers.

The operation of the receiver is additionally controlled by the

signal rx_on which is set high when modulated signal is

expected on the receiver input. This signal is used to control

RSSI and AGC and also enables processing of receiver output

by Framing logic. Signal rx_on is automatically set high after

Mask Receive timer expires. Signal rx_on can also be directly

controlled by the controller by sending direct commands Mask

Receive Data and Unmask Receive Data. Figure 14 illustrates the

Receiver block diagram.

Demodulation Stage

First stage performs demodulation of transponder sub-carrier

response signal, which is superimposed on HF field carrier. Two

different blocks are implemented for AM demodulation: Peak

Detector and AM demodulator mixer. The choice of the

demodulator, which is used, is made by the Receiver

Configuration Register 1 bit amd_sel.

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